"You can't fault that Cantabrian will to be the best and to win - that's what we came here to do and we've done it."
Victory appeared a long way off early on as Northern began brightly. Seeking their fourth title in eight years, the Lights took the lead when Jane Barnett capitalised on some hesitant defending to drive home a strike from just inside the box.
But the minor premiers were in front for only 10 minutes, Longo equalising when the Lights failed to clear a Rennie cross and the Football Ferns playmaker pounced on the loose ball to fire it past keeper Anna Leat, another who starred for the New Zealand under-17s in Uruguay.
Longo had her second just past the half-hour mark when Rennie again caused problems for Northern, picking up an under-hit pass before feeding her captain to slot home from close range for a 2-1 lead.
The South Islanders weren't able to go into the break a goal up, though, with Northern captain Claudia Bunge getting her head to a deep 40th-minute corner to make it 2-2.
The second half failed to live up to the goal-laden excitement of the first but was just as competitive. With the heat taking a toll and many players struggling with heavy legs after recently returning from international duty, few clearcut chances were created and extra time was needed to separate the sides.
Rennie proved a constant threat for Canterbury, with the pacey winger breaking down the right and evading a challenge before crossing for substitute Barker to tuck away what proved the winner towards the end of the first half of extra time.
The Lights piled on the pressure in the closing stages but struggled to find a way through the Pride's resolute defence as the visitors held on to claim another title after losing last year's final to Auckland.
"It's disappointing for us because we felt we could have got more out of the game," Northern coach Gemma Lewis said. "But the girls put a shift in and did everything they could.
"I didn't know if we were going to last extra time but we ended up being the more dominant team and really went for it.
"I'm super-proud of them. It's disappointing but we will reflect on this and I'm sure we'll see it as a successful campaign."
Canterbury United Pride 3 (Annalie Longo 16, 31, Monique Barker 102)
Northern Lights 2 (Jane Barnett 6, Claudia Bunge 40) after extra time.
Halftime: 2-2. Fulltime: 2-2.